Thecal tabulation, body scale morphology and phylogeny of <i>Heterocapsa philippinensis</i> sp. nov. (Peridiniales, Dinophyceae) from the Philippines

Abstract

The thecal tabulation and body scale structure of the marine armoured dinoflagellate <i>Heterocapsa</i>, isolated from Philippines, were examined using LM, SEM and TEM, and its phylogenetic position was inferred from ITS and LSU rDNA sequences. Cells were ovoid and the plate tabulation (Po, cp, X, 5′, 3a, 7′′, 6c, 5s, 5′′′, 2′′′′) was consistent with most <i>Heterocapsa</i> species. The second anterior intercalary plate (2a) had a circular pattern with a thick marginal border free of pores. The nucleus was longitudinally elongated and curved, and located at the dorsal side of the cell. Discoid lobes of brownish chloroplast were peripherally distributed, and a pyrenoid was positioned at the centre. The triradiate body scales, measuring 250–300 nm in diameter, consisted of a roundish basal plate with six radiating ridges, nine peripheral uprights/spines, and three radiating spines. These components were identical to those of <i>H. pseudotriquetra</i> and <i>H. steinii</i>, except for the roundish outline of basal plate. Molecular phylogeny showed that the species clustered with <i>H. pseudotriquetra</i> and <i>H. steinii</i>. This species was differentiated from all other <i>Heterocapsa</i> species in the sausage-shaped nucleus and circular pattern on the 2a plate. This study proposed a novel species <i>Heterocapsa philippinensis</i> sp. nov. for the isolate.